1. Field of the Invention
The present invention relates to a high-frequency module including a multilayer substrate in or on which are provided a first signal path through which an RF signal passes and a second signal path through which an RF signal passes.
2. Description of the Related Art
Thus far, a high-frequency module including high-frequency circuit elements such as switch circuits, duplexers, directional couplers, and the like has been provided. Such a high-frequency module is used as a front-end module connected immediately subsequent to an antenna element, and includes a multilayer substrate 500 such as that illustrated in FIG. 6, for example. FIG. 6 is a diagram illustrating an example of a multilayer substrate included in a past high-frequency module. Here, high-frequency circuit elements such as a directional coupler 501, an inductor 502, a capacitor 503, and a switch circuit transmission line 504 are formed within the multilayer substrate 500 as combinations of internal wiring electrodes such as in-plane conductor patterns and via conductors.
Incidentally, the directional coupler 501 is used, for example, to extract the power of a transmission signal (RF signal) flowing in a main line 501a from a sub line 501b electromagnetically coupled with the main line 501a and monitor that power. There is a risk of the following problem arising in the case where the internal wiring electrodes that form the directional coupler 501 are formed within the multilayer substrate 500 as illustrated in FIG. 6. The internal wiring electrodes that form the directional coupler 501 may electromagnetically couple with the internal wiring electrodes that form the elements aside from the directional coupler 501, such as the inductor 502, the capacitor 503, and the transmission line 504, causing RF signal leakage, interference, and so on. There is also a risk that the characteristics of the directional coupler 501 will vary due to manufacturing variations in the internal wiring electrodes arising when the multilayer substrate 500 is manufactured. Furthermore, because the directional coupler 501 is provided within the multilayer substrate 500, it is difficult to readjust the characteristics of the directional coupler 501 in the case where those characteristics have changed.